This invention relates generally to inflatable restraint systems and, more particularly, to an improved closure for use with an installation of an inflatable cushion, commonly referred to as an air bag.
Safety restraint systems which self-actuate from an undeployed to a deployed state without the need for intervention by the operator, i.e., "passive restraint systems", and particularly those restraint systems incorporating inflatable bags or cushions, as well as the use of such systems in motor vehicles have been the subjects of much discussion as the desirability of the use of such passive restraint systems has gained general acceptance in the United States.
It is well known to protect a vehicle occupant using a cushion or bag that is inflated with gas, e.g., an "air bag", when the vehicle encounters sudden deceleration, such as in a collision. During deployment, the rapidly evolving gas with which the bag is typically filled is an inert gas, e.g., nitrogen. In such systems, the cushion is normally housed in an uninflated and folded condition to minimize space requirements. Upon actuation of the air bag system, gas is discharged from an inflator to rapidly inflate the bag. The cushion, upon inflation, serves to restrain the movement of the vehicle occupant as the collision proceeds. In general, such air bags are commonly designed to be inflated in no more than about 30-60 milliseconds.
Inflatable restraint systems have been devised for automotive vehicles in which one or more air bags are stored in one or more storage compartments within the vehicle. In general, an air bag provided for the protection of a vehicle driver, i.e., a driver side air bag, is stored within a housing mounted in a storage compartment located in the steering column of the vehicle. Whereas, an air bag for the protection of a front seat passenger, i.e., a passenger side air bag, is typically stored within a housing mounted in the instrument panel/dash board of the vehicle. In either case, the housing generally has a cover or some form of closure panel member having a face portion to provide closure to the opening through which the air bag will be deployed upon actuation.
In order to reduce the likelihood of tampering with the system, the closure panel member is commonly designed so as to minimize the visual impression of the presence of the air bag and air bag deployment opening thereunder. Thus, such closure panel members are typically designed to match or otherwise be compatible with the interior design of the vehicle.
Also to this end, appearance or otherwise cosmetic problems such as read through and sink marks are sought to be avoided. Read through (e.g., where shapes or features on the backside of the closure can be relatively easily discerned from a viewing of the front side of the closure) and sink marks (e.g., where the closure has an undesired, lower or uneven outer surface) can result from processing. For example, when the closure is prepared by molding fabrication of a thermoplastic elastomer, an uneven shrinkage of the closure material upon processing can result in read through and/or sink marks.
In practice, closure panel members are commonly designed so as to be torn or otherwise opened along predetermined lines as a result of the force exerted against the closure by way of the inflating air bag and thus form air bag release doors. To this end, the closure is typically pre-weakened, such as by perforating or reducing the thickness of the cover, for example, along such preformed tear lines, paths or seams, generally commonly referred to herein as "tear ways".
In many previous designs, the tear ways are typically of uniform strength, e.g., the tear ways are of uniform thickness and consistency, throughout the closure. As a result, the location of the initial tearing or opening of the closure can typically vary, depending largely upon the manner in which the force of the inflating air bag is applied against the closure which in turn is largely dependent upon the way in which the air bag is folded as well as the conditions under which the system is being used. For example, tearing of the tear way may undesirably start at a location near the end of the respective tear way, e.g., near the edge of the face portion of the closure. As will be appreciated, the manner in which the closure is torn can detrimentally affect the manner in which the air bag is inflated and the shape or form taken thereby, and thus result in inflation of the bag in a non-optimal manner.
Thus, in order to be able to effect the deployment in an orderly process it is desirable to be able to control the point or location of the initial opening in the closure, wherethrough the air bag first begins deployment into the passenger compartment of the vehicle.
One approach has been to vary or alter the strength, e.g., the thickness and/or consistency, of a respective tear way in the closure. For example, U.S. Pat. No. 5,013,065 discloses the use of a rupturable cover of continuously increasing thickness and having rated break lines therein. U.S. Pat. No. 5,060,971 discloses varying the strength of the weakened zones, e.g., tear lines, such as by: 1) using rows of spaced-apart grooves along the weakened zone with the grooves being more closely spaced together at the initial opening location, 2) using grooves along the weakened zone with deeper grooves, i.e., thinner cover, at the initial opening location, and 3) using interconnected grooves consisting of spaced-apart deeper grooves of substantially uniform size and shape and shallower grooves in spaces between the deeper grooves with the deeper grooves being closer together in the initial opening area.
In addition, a number of patents identify various groove geometries for fracture lines, hinges and other portions of air bag covers. For example, U.S. Pat. No. 3,622,176 discloses using V-shaped grooves along the fracture lines and hinge elements having rounded root grooves, so as to avoid fracture. Other or similar cover groove geometries are shown in other patents including U.S. Pat. No. 4,964,652; 5,002,307; 5,069,477; 5,087,071; and 5,143,401.
A common problem with approaches wherein the thickness of the tear ways of the closure are specially altered or varied along the length thereof, such as at the site of initial opening is that closures with particularly thin tear ways, such as those tear ways having sections or portions such as tear ways of a thickness of 0.35 mm or less, are commonly more susceptible to failure due to fatigue and consequent inadvertent or accidental opening as well as undesired opening such as may result from tampering. Furthermore, with molded closures such particularly thin initial opening sites are more likely to be visible to an occupant which is generally aesthetically undesirable.
In addition, the inclusion in a closure of a pre-weakened initial opening site typically results in such closure being invariably more difficult to manufacture as items having such thin sections are, for example, difficult to form via molding fabrication.
In contrast to tear ways of substantially uniform thickness, tear ways with graduated or steadily varying thickness while typically providing greater control over the closure opening process including the site of the initial opening, increase the likelihood of certain undesirable forms of closure tearing, such as tearing outside of the tear path. For example, when a closure is undergoing tearing along a tear path and the tearing action reaches a point in the tear way at which there is an abrupt increase in the thickness of the tear way, the abrupt change in thickness can result in tearing outside of the tear path. In the case of a tear way of gradually increasing thickness, as the thickness of the tear way increases, the difference in thickness of material at the tear way and the adjacent sections of the face portion diminishes, increasing the likelihood of non-tear way tearing of the closure.